<script language="javascript" type="text/javascript">
function validate_login(){
    if(document.login.user.value=='Email đăng nhập:'){
        alert ('Thông tin bắt buộc!');
        document.login.user.focus();
        return false;
    }
    if(document.login.pass.value=='Mật khẩu:'){
        alert ('Thông tin bắt buộc!');
        document.login.pass.focus();
        return false;
    }
    return true;
}
<?php if($this->CALL_SCRIPT):?>                

    $(function(){
        <?php echo $this->CALL_SCRIPT;?>
    });

<?php
$this->CALL_SCRIPT =''; 
endif;?> 
</script> 
<form action="" method="post" name="login">
    <input name="hidden_login" type="hidden" value="login"/>
	<ul class="login_list">
    	<li><input type="text" size="20" id="user" name="user" class="watermark user" watermark="Email đăng nhập:" value="" /></li>
        <li><input type="password" size="20" id="pass" name="pass" class="watermark pass" watermark="Mật khẩu:" value="" /></li>
    </ul>
    <p class="login_link"><a href="/reset-password/" class="forget">Bạn quên mật khẩu?</a>
        <a href="javascript:void(0);" class="btn_click" onclick="if(validate_login()) document.login.submit();"><span>Đăng nhập</span></a>
        <a href="/register/" class="btn_click" ><span>Đăng ký</span></a>
    </p>
</form>